Method for separation and removal of suspended liquid particles from molten metal and associated apparatus

ABSTRACT

Molten metal containing suspended liquid particles is passed preferably generally upwardly through a porous media so constructed and arranged such that the movement of the molten metal therethrough renders the suspended liquid particles gravity separable. The gravity separable liquid particles rise upwardly or settle downwardly so as to be removable from said molten metal for subsequent removal therefrom. An associated apparatus is also provided.

BACKGROUND OF THE INVENTION

This invention relates to separating and removing suspended liquidparticles from molten metal by passing the molten metal containing thesuspended liquid particles preferably generally upwardly through aporous media. The porous media is constructed and arranged such that themovement of the molten metal therethrough renders the suspended liquidparticles gravity separable.

Molten metal, such as aluminum, including alloys containing over 50%aluminum, has been treated to remove impurities therefrom. Some of thesetreatments, such as in furnace fluxing or in-line treatment, generateliquid particles, such as molten salts. Also, additions of salts areoften made to furnaces to reduce melt loss. A portion of these moltensalts are carried along with the molten metal and, if not removed fromthe molten metal, can create "oxide patches" on the surface of thesolidifying ingot. These oxide patches not only adversely affect ingotquality but also many times have to be scalped off of the ingot, whichresults in a reduction of the recovery of metal in the ingot castingoperation. Oxide patches can also cause ingots to crack. In some cases,the oxide patches are so prevalent that the entire ingot must bescrapped and remelted. This, of course, adds cost to the ingot castingoperation.

The liquid particles referred to, such as the molten salts, are in themicron size range, typically from less than 1 micron up to 80 orpossibly 100 microns in size. The molten salts are usually MgCl₂, NaCl,CaCl₂, KCl, LiCl and mixtures thereof. The molten salts can also containNaF, AlF₃ and CaF₂ originating from furnace additives or potroom metal.Most liquid salts are lighter than the molten metal and would be gravityseparable but remain entrained or suspended largely because their smallsize results in an extremely slow rise velocity. Other than for theirsmall size, the buoyant liquid particles would rise to the surface forremoval by skimming or similar operations.

There have been efforts to remove particles, such as solid and liquidinclusions, from molten metal. U.S. Pat. No. 4,390,364 discloses aremoval method comprising moving the molten metal containing suspendedparticles downwardly through a medium of submerged contacting surfacessuch as a packed bed. The contacting medium has a high void fraction anda high specific surface area. The patent states that this results incoalescence or agglomeration of the suspended particles. After this, themolten metal is passed generally downwardly through inclined channels orpassages. Buoyant particles and agglomerates collect on the underside ofthe inclined surfaces and typically move upward in a counter-flowrelationship with the metal, where the metal moves laterally anddownwardly through the inclined passages. These buoyant particles andagglomerates are removed by skimming or similar operations.

U.S. Pat. No. 4,790,873 discloses a method of removing particles frommolten metal by contacting the molten metal with a medium which retainsmetal-nonwettable inclusions and then passing the molten metal through afilter of metal-wettable material. The metal-wettable material of thefilter retains the liquid particles therein. The filter containing theliquid particles is subsequently removed and replaced.

Despite these known methods and apparatus, there remains a need for animproved method for separation and removal of liquid particles frommolten metal.

SUMMARY OF THE INVENTION

The invention has met the above-described need. In accordance with theinvention, molten metal containing liquid particles suspended thereincan be treated by passing the same through a porous media so constructedand arranged such that the movement of the molten metal therethroughrenders the suspended liquid particles gravity separable. Preferably,the molten metal is passed generally upwardly through the porous media.In this way, the gravity separable liquid particles rise upwardly so asto be removable from the molten metal. In one aspect of the invention,the porous media is so constructed and arranged to facilitatecoalescence of the suspended liquid particles on the porous media. Thecoalesced liquid particles are carried out of the porous media bysufficient molten metal velocity and by creating coalesced liquidparticles having increased buoyancy over the original smaller Suspendedliquid particles. The porous media may also filter out some solidparticles.

In an embodiment of the invention, the porous media is made of a porousceramic material which has preferably 10 to 60 pores per inch and morepreferably 20 to 40 pores per inch. In another embodiment the porousmedia can have an upper portion and a lower portion, the lower portionhaving more pores per inch than the upper portion. In this way, thelower portion can facilitate coalescence of the liquid particles whilethe upper portion facilitates carrying away of the coalesced liquidparticles out of the porous media. In yet another embodiment of themethod, a filter can be provided downstream of the porous media tofurther capture remaining liquid and solid particles in the molten metalflowing through the filter.

An associated apparatus is also provided which comprises a molten metalpassageway having mounted generally horizontally therein a porous mediaarranged such that the molten metal passes generally upwardly throughthe porous media. The porous media is so constructed and arranged suchthat movement of the molten metal therethrough renders the suspendedliquid particles gravity separable, whereby the gravity separable liquidparticles rise upwardly to the upper surface of the molten metal. Themolten metal passageway has an inlet portion upstream of the porousmedia and a settling zone downstream of the inlet portion. The settlingzone has sufficient length in relation to molten metal velocity anddepth of molten metal to allow the gravity separable liquid particles tofloat to the top surface of the molten metal in the settling zone.

It is an object of the invention to remove liquid particles from moltenmetal before casting of the molten metal into ingots.

It is a further object of the invention to provide a method andapparatus which creates gravity settlable liquid particles from liquidparticles suspended in the molten metal.

It is yet another object of the invention to provide a porous mediawhich is constructed and arranged so as to facilitate coalescence ofliquid particles therein for subsequent carrying out by the molten metaland ultimate removal from the molten metal surface by skimming or a likeoperation.

It is still another object of the invention to provide a liquid particleremoval method and apparatus that will result in increasing the usefullifetime of the bed filter and/or other filtration systems used in thecasting process.

These and other objects of the invention will be more fully understoodfrom the following description of the invention with reference to thedrawings appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view depicting the operation of the improved systemshowing one arrangement suitable for practicing the invention.

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1.

FIGS. 3-6 are enlarged cross-sectional views of the porous media, in atime lapse sequence, showing the coalescing and subsequent release fromthe media of the liquid particles.

FIG. 7 is a schematic drawing showing a porous media with an upperportion and a lower portion having different pore sizes.

FIG. 8 is a schematic view of two liquid inclusions, showing thedifference between a wetting and a non-wetting surface.

FIG. 9 is a graph showing the terminal rise velocity as a function ofthe particle diameter.

FIG. 10 is a photomicrograph (100x) of an inclusion sample takenupstream of the porous media for the first example.

FIG. 11 is a photomicrograph (100x) of an inclusion sample takendownstream of the porous media for the first example.

FIG. 12 is a photomicrograph (100x) of an inclusion sample takenupstream of the porous media for the second example.

FIG. 13 is a photomicrograph (100x) of an inclusion sample takendownstream of the porous media for the second sample.

DETAILED DESCRIPTION

The method and apparatus of the invention operates in association withthe process of casting molten metal, such as aluminum and aluminumalloys, into ingots. As is well known to those skilled in the art, asource of aluminum is provided and melted in a furnace and thentransferred to a holding furnace. The molten metal is then oftensubjected to a fluxing and/or filtering treatment. The filteringtreatment removes entrained solid particles such as aluminum oxideparticles and the fluxing treatment is used to remove dissolved hydrogenas well as lowering the content of metals such as sodium, calcium andmagnesium. However, when chlorine or chlorine-containing reactants areused, the fluxing treatment can form liquid particles, such as moltensalts e.g. MgCl₂. A fraction of the molten salt in the melt can remainas a very finely divided suspension and can be difficult to remove orseparate from the molten aluminum by flotation or gravity separation.That is, even though the molten salt may have a lower density than thealuminum, some remains entrained therein and can pass through thefiltering system with the resulting imperfections in the cast aluminumingot.

Referring now to FIGS. 1 and 2, the improved liquid particle removalsystem includes a containment vessel 12 constructed or lined with asuitable refractory material in which the molten metal 11 is contained.The containment vessel 12 includes two sidewalls 13, 14 (FIG. 1) as wellas a floor 15 (FIG. 2). A lid (not shown) can be provided to cover thecontainment vessel 12. An inlet baffle 18 establishes an inlet leg 20for the flow of molten metal (shown by the arrows in FIGS. 1 and 2). Arigid porous ceramic media 24 is mounted generally horizontally in thecontainment vessel 12 such that the molten metal entering the inlet leg20 is passed generally upwardly therethrough, as seen best in FIG. 2.

The containment vessel 12 further includes an outlet baffle 28 whichestablishes an outlet leg 30. The inlet baffle 18 and outlet baffle 28define a settling zone 32 where the gravity separable liquid particles,shown in FIG. 2 as coalesced liquid particle globules 34, are collectedon the upper surface 35 of the molten metal 11. The settling zone 32includes a floor 36 supported by walls 37 and 38 (FIG. 2) mounted to thefloor 15 of the containment vessel 12. A porous ceramic filter 40 ismounted generally horizontally in the floor 36 such that the moltenmetal in the settling zone area 32 passes generally downwardlytherethrough.

Referring more particularly to FIG. 2, in operation, liquid particles50, typically salt particles less than one micron to possibly fiftymicrons, are entrained in the molten metal 11 flowing in the inlet leg20 upstream of the rigid porous ceramic media 24. As used herein, theterm "liquid particles" also includes slurries of liquid particles andsolids, the solids being less than about fifteen volume percent of theliquid particles. More generally, the term liquid particles meansparticles which are deformable to the shear forces experienced inconventional trough and filter arrangements. The liquid particles aretypically lighter than the molten metal, but are not gravity separableand remain entrained or suspended largely because of the very low risevelocity caused by their small size. The liquid particles can includemolten salts such as MgCl₂, NaCl, CaCl₂, KCl, LiCl and mixtures thereof.The molten salts can also contain fine solids, such as NaF, AlF₃ andCaF₂ originating from furnace additives or potroom metal. The fluorides,in addition to being solids, can also be dissolved in the molten salt.Furthermore, the liquid particles can be liquid metal phases insolublein aluminum, such as Pb.

As can be seen by the arrows in FIGS. 1 and 2, the molten metal 11containing the liquid particles 50 passes generally upwardly through therigid porous ceramic media 24. As will be explained in greater detailwith respect to FIGS. 3 to 6 below, as the liquid particles passgenerally upwardly through the rigid porous ceramic media 24, the rigidporous ceramic media 24 renders the liquid particles gravity separablewith the gravity separable liquid particles subsequently being releasedfrom the media 24. Once released, the liquid particle globules 34, dueto their greater buoyancy and the generally upward molten metal flowvelocity, float to the top surface 35 of the molten metal 11 in thesettling zone 32 as shown in FIG. 2. The liquid particle globules 34 aretypically over 50 or 60 microns and as large as 1,000 microns or larger.From there, floating liquid particle globules 34 can be periodicallycollected and removed from the containment vessel 12 by skimming orother like operations.

As can be seen in FIG. 2, a small percentage of the liquid particles 62may remain entrained in the molten metal 11 after it is passed throughrigid porous ceramic media 24. This can be caused by the fact that someliquid particles may not be coalesced in the rigid porous ceramic media24 and because, as will be discussed with respect to FIG. 6, as thelarge coalesced particles are released from the rigid porous ceramicmedia 24, some smaller diameter droplets of liquid particles can begenerated. This happens because in the release process, the film of theliquid particles is ruptured. In order to further remove these liquidparticles 62, the molten metal containing these liquid particlesoptionally can be passed through the porous ceramic filter 40. Liquidparticles 62 that remain trapped in the porous ceramic filter 40 can beremoved when the filter 40 is replaced, which usually occurs after eachcasting of molten metal (one casting typically ranging fromapproximately 40,000 to 250,000 pounds of metal). The porous ceramicfilter 40 can also capture remaining solid particles in the moltenmetal.

Filter 40 can be similar to porous media 24. However, preferably, filter40 has a greater number of pores per inch (see discussion hereinafterfor the meaning of pores per inch) than media 24 to capture the smallerliquid particles that remain entrained in the molten metal 11 after themolten metal 11 is passed through media 24. As porous media 24 effectsremoval of substantially most of the liquid particles in the moltenmetal 11, filter 40 is usually not loaded by the liquid particles (aswill be explained and shown with respect to FIGS. 4-6) and thus does notcreate globules of liquid particles that are released therefrom. Filter40, thus, is used to capture liquid particles which remain entrained inthe molten metal 11 after passing generally upwardly through porousmedia 24.

The invention contemplates using the rigid porous ceramic media 24,which will render gravity separable substantially most of the liquidparticles 50 entrained in the molten metal 11 while omitting the use ofporous ceramic filter 40. It will be further appreciated that thecontainment vessel 12 could be configured such that the molten metalwill also flow generally upwardly through the porous ceramic filter 40;however, this is not as preferred because this would mean that thesettling zone 32 would be shorter (for the same containment vessellength) or the containment vessel size would have to be increased (forthe same settling zone length).

The rigid porous ceramic media 24 can be made of several types ofmaterials such as, for example, ceramic foams, bonded ceramicparticulate, porous carbon and glasses. The ceramic foam media can beproduced by using a polyurethane precursor which is immersed in aceramic slurry and then fired at a high temperature. During firing, thepolymer precursor vaporizes leaving a sintered or fused ceramic media.The bonded ceramic particulate media consists of tabular ceramic mediaheld together by a ceramic binder or by bonds formed by sinteringwithout a binder.

Rigid porous ceramic media is commercially available from variousmanufacturers such as Hi-Tech Ceramics, Inc. of Alfred, N.Y. sold underthe trade name Alucel™. These media are generally composed of mixturesof oxides such as alumina, zirconia and silica. The alumina filters, inparticular, can be sintered or phosphate bonded.

As is known to those skilled in the art, a standard measurement of poresize of a porous ceramic media is described by the number of pores perlinear inch or PPI. The PPI of a specific media is determined, for foammedia, from the original pore size of the polyurethane foam used as theprecursor. Although a variation in pore size can occur, an average PPIcan usually be determined and since the pores are nearly spherical inshape, their size can be represented by an effective diameter. The poresizes for the media used in the present invention are preferred to be inthe range of about 10 to 60 PPI with 20 to 40 PPI being more highlypreferred.

Referring now to FIGS. 3 to 6, a detailed view of the operation of therigid porous ceramic media 24 is shown. The molten metal 11 containingliquid particles 50 is passed generally upwardly through the media 24(as indicated by the flow direction arrows), and because the media 24 iswettable by the liquid particles 50, they can wet the media 24 as isshown by the stippled areas 70 on the media 24 in FIG. 3. This wettingwill continue until most of the media 24 is wetted as shown in FIG. 4.Once this occurs, the liquid particles will start to move upwardly as aviscous liquid flow by virtue of the molten metal flow and willeventually gather on the upper surface of the media 24 as shown in FIG.5 by the retained coalesced liquid particles 75. This will continueuntil the surface effects of the coalescing liquid particles cause thecoalesced particles to become buoyant and start to lose contact with themedia 24 as shown by coalesced liquid particle globules 34 shown in FIG.6 and in FIGS. 1 and 2. The size of these coalesced liquid particleglobules 34 is on the order of about 100 to 10,000 microns, with mostbeing greater than 500 microns. At this size, the coalesced liquidparticle globules 34 are gravity separable and then rise through themolten metal 11 in the settling zone 32. It can also be seen from FIG. 6that some smaller liquid particles, such as particles 62 (see also FIG.2), can be released when the larger liquid particle globules 34 arereleased. This is believed to be because in the release process, thefilm of the liquid particles is ruptured which creates these smallerliquid particles 62. Nonetheless, the amount of such smaller liquidparticles 62 is drastically reduced over the amount of smaller liquidparticles 50 carried by the molten metal entering the system.

Referring now to FIG. 7, in another embodiment, the ceramic media canconsist of an upper portion 90 and a lower portion 92, the upper portionhaving less average PPI (such as 10 to 20 PPI) than the lower portion(such as 30 to 40 PPI). In this way, the liquid particles are capturedmore easily on the lower portion 92 for coalescence and subsequently thecoalesced particles can pass more easily through the upper portion 90.

As was mentioned above, the ceramic media is wettable by the liquidparticles sought to be removed. One narrow test for determining whethera media is wettable or not involves heating the media to about 600°-700°C. and pouring a heated liquid salt on the media. If the liquid saltbeads on the media, the media is non-wettable. If the liquid salt doesnot bead, the media is wettable. In a narrower test, if the heatedliquid salt is poured on a heated media and passes through or spreads(but does not bead) the media is also wettable. A more broad testinvolves measuring wettability as a function of the interfacial tensions(measured in dynes per centimeter) between the ceramic media, the moltensalt and the molten aluminum. FIG. 8 illustrates partially schematicallythe concept of wettability and non-wettability. The molten salt-solidsubstrate (in this case the ceramic media) interfacial tension isindicated by the variable γsl, the molten salt-molten aluminuminterfacial tension is indicated by the variable γsv and the moltenaluminum-solid substrate interfacial tension is indicated by γlv. If γslis greater than γsv, then the angle θ, which is determined by theYoung-Dupre equation ##EQU1## will be greater than 90° and the moltensalt will be non-wetting toward the substrate. In this case, the moltensalt will have no tendency to spread on the ceramic media surface butinstead the molten aluminum will spread over the ceramic media inpreference to the molten salt. If γsl is less than γsv, then θ will beless than 90° and the molten salt will be wetting toward the substrateand the molten salt, as opposed to the molten aluminum, will tend tospread over the ceramic media surface.

The minimum length of the settling zone 32 (FIGS. 1 and 2) is determinedto accommodate gravity settling of the liquid particles to the topsurface of the molten metal 11 so that the coalesced liquid particleglobules 34 can be skimmed or otherwise removed from the top surface ofthe molten metal. As can be seen on the graph shown in FIG. 9, thelarger the liquid particle globule diameter, the faster the risevelocity. Therefore, for larger particles the settling zone 32 (assumingconstant width, depth and metal flow velocity) can be shorter in orderfor the liquid particle globules to rise to the top surface of themolten metal.

Referring in more detail to FIG. 9, the relationship between theparticle diameter (measured in microns) plotted on the x-axis and therise velocity of the particle (measured in cm/sec) plotted on the y-axisis shown. The values on this graph are calculated using Stokes Law, withthe viscosity (n) of aluminum being equal to 1.2 cp and the densitydifference (ρm-ρs) between the aluminum and the liquid particle being0.05 g/cm³. FIG. 9 clearly shows that rise velocity increasessubstantially as the particle diameter becomes larger. As an example,assuming a coalesced liquid particle size of 1,000 μm, from FIG. 9, therise velocity will be 2.3 cm/sec. As the rise velocity increases, thecoalesced liquid particles will need less distance in the molten metalflow direction to rise to the surface of the molten metal in thesettling zone 32 (FIG. 1).

While the foregoing description has emphasized the improvement asapplied to treating molten aluminum, such is not necessarily intended tolimit the scope of the improvement herein described which applies to thelight metal magnesium and to other metals. While considerable emphasishas further been placed on passing the molten metal generally upwardlythrough the porous media and the liquid particles rising upwardly to thesurface of the molten metal, the invention also encompasses passing themolten metal generally downwardly or generally laterally through theporous media and also encompasses the liquid particles being renderedgravity separable by sinking downwardly for subsequent removal from themolten metal passageway where the density of the particle phase isgreater than the molten metal.

EXAMPLES

To demonstrate the concept, a test was run with aluminum alloy 5182. Aquantity of 10,000 lb of alloy was melted in a gas-fired furnace.Phosphate-bonded alumina foam media (30 PPI, 12"L×12"W×2"D) were used inboth the upstream and downstream positions of a unit similar to FIG. 1.The alumina foam media had 30 PPI. The metal in the furnace was heatedto approximately 1350° F. At some given time, the plug was removed fromthe furnace taphole and metal flowed from the furnace into a connectingtrough and then into the unit. As soon as metal flow was begun, moltensalt of composition 70% MgCl₂ -30% NaCl was semi-continuously pouredonto the metal surface and stirred in for dispersal with a graphitestirrer, the additions being made immediately upstream of the unit.Initially, no liquid salt particles were observed on the metal surfacein the unit or downstream of the unit. After twenty-eight minutes ofoperation, large releases of liquid salt particles floated to the metalsurface above the upstream media. Regular releases of liquid saltparticles occurred throughout the remainder of the test. These liquidsalt particles could be skimmed off the metal surface at this point. Thetest continued for approximately 1 hour at a flowrate of 7,000 lb/hr.This test demonstrated that the salt added and dispersed upstream of theinvention was coalesced in the first media, was released from the mediain a coalesced state and then floated to the surface of the molten metalin the settling zone. The salt was not carried downstream of the firstmedia, so it did not end up in the final product. Inclusions sampleswere taken both upstream of the first media 24 and downstream of thesecond media 40, to demonstrate its ability to remove salt.

The procedure to take an inclusion sample was to pull molten aluminum,by a vacuum of approximately 25 in. of mercury, through a porous carbondisk. After approximately 0.5 to 1 kg of aluminum was passed through theporous carbon, the cartridge containing the porous carbon was removedfrom the metal being supplied and allowed to solidify. The porous carbondisk was then sectioned and examined metallographically. Any solid orliquid inclusion present in the metal were collected on the surface ofthe porous carbon disk.

FIG. 10 shows a photomicrograph of an inclusion sample taken upstream ofthe first media. The existence of round holes 101 in the metallicportion 100 of the sample, grey staining of the metal 102, and roundrings 103 are the results of salt present in the sample. A portion ofthe carbon 104 from the inclusion sample cartridge can also be seen. Thegrey staining of the sample is the result of atmospheric moisturebecause of the hygroscopic nature of the salt present in the sample.FIG. 11 shows a photomicrograph of an inclusion sample taken downstreamof the second media. The metallic portion 110 is relatively clean withlittle, if any, salt 111 present. The voids 112 in the sample aresolidification, shrinkage cavities and, in addition, some constituentphase 113 can also be seen. The carbon 114 from the inclusion samplecartridge is also present in FIG. 11. No grey staining of the sampleoccurred, and round voids indicative of salt were not present. Thismetallographic analysis of inclusion samples indicates that theinvention effectively removes salt particles from the stream of moltenaluminum.

In a second example, conditions were the same as the first exampleexcept mullite-bonded alumina media (1.5 in. thick) were used and themetal flowrate through the unit was 11,000 lb/hr. Releases of moltensalt above the upstream media element were observed 19 minutes aftersalt additions upstream of the entire unit were begun. FIG. 12 is aphotomicrograph of an inclusion sample taken upstream of the unit. Themetallic portion 140 contains evidence of salt due to the condenseddroplets of water 141 and the grey staining 142. Constituent metallicphase 143 and shrinkage cavities 144 are also present as well as thecarbon 145 from the inclusion sample cartridge. FIG. 15 shows aphotomicrograph of an inclusion sample taken downstream of the secondmedia. Once again, there is little or no evidence of the presence ofsalt in the metallic portion 150. Constituent metallic phase 151 andshrinkage cavities 152 as well as the carbon 153 from the inclusionsample is shown.

The photomicrographs in FIGS. 10-13 show that the apparatus and themethod of the invention are effective for removing molten salts frommolten aluminum. While it will be appreciated that the examples haveshown removal of molten salts from molten aluminum, the invention is notlimited to molten aluminum and can be used with other light moltenmetals such as magnesium.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass allembodiments which fall within the spirit of the invention.

What is claimed is:
 1. A method of treating molten metal containingsuspended liquid particles, said method comprising:passing said moltenmetal containing said liquid particles through a porous media that iswettable by said suspended liquid particles such that said movement ofsaid molten metal therethrough renders said suspended liquid particlesgravity separable, whereby said gravity separable liquid particles riseupwardly or settle downwardly so as to be removable from said moltenmetal.
 2. The method of claim 1, whereinsaid porous media is made ofmaterials selected from the group consisting of oxides of alumina,zirconia, silica and mixtures thereof.
 3. The method of claim 1,whereinsaid porous media contains phosphate bonded alumina.
 4. Themethod of claim 1, whereinsaid porous media contains sintered alumina.5. The method of claim 1, whereinsaid porous media has an average ofbetween about 10 to 60 pores per inch.
 6. The method of claim 5,whereinsaid porous media has an average of between about 20 to 40 poresper inch.
 7. The method of claim 1, whereinsaid porous media has anupper portion and a lower portion, said upper portion having lessaverage pores per inch than the average pores per inch of said lowerportion.
 8. The method of claim 7, whereinsaid upper portion has about10 to 20 pores per inch and said lower portion has about 30 to 40 poresper inch.
 9. The method of claim 1, whereinsaid molten metal iscontained in a molten metal passageway having an inlet portion upstreamof said porous media and a settling zone downstream of said inletportion; and said settling zone having sufficient length in relation tothe velocity of the molten metal in said settling zone and the depth ofsaid settling zone to allow said gravity separable liquid particles tofloat to the top surface of said molten metal in said settling zone assaid molten metal moves through said settling zone.
 10. The method ofclaim 9, includingafter passing said molten metal through said porousmedia, passing said molten metal through a filter media to capturesuspended liquid particles remaining in said molten metal.
 11. Themethod of claim 1, includingafter passing said molten metal through saidporous media, passing said molten metal through a filter media tocapture suspended liquid particles remaining in said molten metal.
 12. Amethod of treating molten metal containing suspended liquid particles,said method comprising:passing said molten metal containing said liquidparticles generally upwardly through a porous media so constructed andarranged such that said movement of said molten metal therethroughrenders said suspended liquid particles gravity separable, whereby saidgravity separable liquid particles rise upwardly so as to be removablefrom said molten metal.
 13. The method of claim 12, whereinsaid porousmedia is wettable by said suspended liquid particles.
 14. The method ofclaim 12, whereinsaid porous media is made of materials selected fromthe group consisting of oxides of alumina, zirconia, silica and mixturesthereof.
 15. The method of claim 12, whereinsaid porous media containsphosphate bonded alumina.
 16. The method of claim 12, whereinsaid porousmedia contains sintered alumina.
 17. The method of claim 12, whereinsaidporous media has an average of between about 10 to 60 pores per inch.18. The method of claim 17, whereinsaid porous media has an average ofbetween about 20 to 40 pores per inch.
 19. The method of claim 12,whereinsaid porous media has an upper portion and a lower portion, saidupper portion having less average pores per inch than the average poresper inch of said lower portion.
 20. The method of claim 19, whereinsaidupper portion has about 10 to 20 pores per inch and said lower portionhas about 30 to 40 pores per inch.
 21. The method of claim 12,whereinsaid molten metal is contained in a molten metal passagewayhaving an inlet portion upstream of said porous media and a settlingzone downstream of said inlet portion; and said settling zone havingsufficient length in relation to the velocity of the molten metal insaid settling zone and the depth of said settling zone to allow saidgravity separable liquid particles to float to the top surface of saidmolten metal in said settling zone as said molten metal moves throughsaid settling zone.
 22. The method of claim 21, includingafter passingsaid molten metal through said porous media, passing said molten metalthrough a filter media to capture suspended liquid particles remainingin said molten metal.
 23. The method of claim 12, includingafter passingsaid molten metal through said porous media, passing said molten metalthrough a filter media to capture suspended liquid particles remainingin said molten metal.
 24. A method of treating molten metal containingsuspended liquid particles, said method comprising:passing said moltenmetal containing said suspended liquid particles generally upwardlythrough a porous media so constructed and arranged to facilitatecoalescence of said suspended liquid particles on said porous media; andcarrying said coalesced liquid particles out of said porous media bysufficient molten metal velocity and by creating coalesced liquidparticles having increased buoyancy over said suspended liquidparticles.
 25. The method of claim 24, whereinsaid porous media iswettable by said suspended liquid particles.
 26. The method of claim 24,whereinsaid porous media is made of materials selected from the groupconsisting of oxides of alumina, zirconia, silica and mixtures thereof.27. The method of claim 24, whereinsaid porous media contains phosphatebonded alumina.
 28. The method of claim 24, whereinsaid porous mediacontains sintered alumina.
 29. The method of claim 24, whereinsaidporous media has an average of between about 10 to 60 pores per inch.30. The method of claim 29, whereinsaid porous media has an average ofbetween about 20 to 40 pores per inch.
 31. The method of claim 24,whereinsaid porous media has an upper portion and a lower portion, saidupper portion having less average pores per inch than the average poresper inch of said lower portion.
 32. The method of claim 1, whereinsaidupper portion has about 10 to 20 pores per inch and said lower portionhas about 30 to 40 pores per inch.
 33. The method of claim 24,whereinsaid molten metal is contained in a molten metal passagewayhaving an inlet portion upstream of said porous media and a settlingzone downstream of said inlet portion; and said settling zone havingsufficient length in relation to the velocity of the molten metal insaid settling zone and the depth of said settling zone to allow saidgravity separable liquid particles to float to the top surface of saidmolten metal in said settling zone as said molten metal moves throughsaid settling zone.
 34. The method of claim 33, includingafter passingsaid molten metal through said porous media, passing said molten metalthrough a filter media to capture suspended liquid particles remainingin said molten metal.
 35. The method of claim 24, includingafter passingsaid molten metal through said porous media, passing said molten metalthrough a filter media to capture suspended liquid particles remainingin said molten metal.
 36. A method of treating molten metal containingsuspended liquid particles, said method comprising:passing said moltenmetal containing said suspended liquid particles generally upwardlythrough a porous media having an average of between 10 to 60 pores perinch such that said suspended liquid particles are rendered gravityseparable, whereby said gravity separable liquid particles rise upwardlyso as to be removable from said molten metal.
 37. The method of claim36, whereinsaid porous media has an average of between 20 to 40 poresper inch.
 38. A method of removing liquid particles suspended in moltenmetal, said method comprising:passing said molten metal containing saidsuspended liquid particles generally upwardly through a porous media soconstructed and arranged such that movement of said molten metaltherethrough renders said suspended liquid particles gravity separable,whereby said gravity separable liquid particles rise upwardly to anupper surface of said molten metal; and periodically collecting andremoving said gravity separable liquid particles from said upper surfaceof said molten metal.
 39. The method of claim 38, whereinsaid removingstep includes skimming said molten metal including said gravityseparable liquid particles from said upper surface of said molten metal.40. A method of treating molten metal containing suspended liquidparticles comprising:passing said molten metal containing said liquidparticles generally upwardly through a porous media so constructed andarranged such that said movement of said molten metal therethroughrenders said suspended liquid particles gravity separable so that saidgravity separable liquid particles can rise upwardly; moving said moltenmetal containing said gravity separable liquid particles generallyhorizontally through a settling zone wherein said gravity separableliquid particles rise to the top surface of said molten metal so as tobe removable from said molten metal; and passing said molten metalgenerally downwardly through a filter media to capture suspended liquidparticles that do not rise to the top surface of said molten metal insaid settling zone.
 41. The method of claim 40, whereinsaid settlingzone has sufficient length in relation to the velocity of the moltenmetal in said settling zone and the depth of said settling zone to allowsaid gravity separable liquid particles to float to said top surface ofsaid molten metal in said settling zone as said molten metal movesthrough said settling zone.
 42. A method of treating molten metalcomprising:treating said molten metal with a chlorinaceous substance,said treatment creating liquid salt particles suspended in said moltenmetal; passing said molten metal containing said suspended liquid saltparticles generally upwardly through a porous media so constructed andarranged such that said movement of said molten metal therethroughrenders said suspended liquid particles gravity separable so that saidgravity separable liquid particles can rise upwardly; moving said moltenmetal containing said gravity separable liquid particles generallyhorizontally through a settling zone wherein said gravity separableliquid particles rise to the top surface of said molten metal so as tobe removable from said molten metal; and passing said molten metalgenerally downwardly through a filter media to capture suspended liquidparticles that were not made gravity separable by said porous media. 43.The method of claim 42, whereinsaid settling zone has sufficient lengthin relation to the velocity of the molten metal in said settling zoneand the depth of said settling zone to allow said gravity separableliquid particles to float to said top surface of said molten metal insaid settling zone as said molten metal moves through said settlingzone.
 44. An apparatus for treating molten metal containing suspendedliquid particles comprising:a molten metal passageway; and a porousmedia that is wettable by said suspended liquid particles mountedgenerally horizontally in said passageway such that said molten metalpasses generally upwardly through said porous media; said porous mediaso constructed and arranged such that movement of said molten metaltherethrough renders said suspended liquid particles gravity separable,whereby said gravity separable liquid particles rise upwardly to theupper surface of said molten metal.
 45. The apparatus of claim 44,whereinsaid porous media is made of materials selected from the groupconsisting of oxides of alumina, zirconia, silica and mixtures thereof.46. The apparatus of claim 44, whereinsaid porous media containsphosphate bonded alumina.
 47. The apparatus of claim 44, whereinsaidporous media contains sintered alumina.
 48. The apparatus of claim 44,whereinsaid porous media has an average of between about 10 to 60 poresper inch.
 49. The apparatus of claim 48, whereinsaid porous ceramicmedia has an average of between about 20 to 40 pores per inch.
 50. Theapparatus of claim 44, whereinsaid porous media has an upper portion anda lower portion, said upper portion has less average pores per inch thanthe average pores per inch of said lower portion.
 51. The apparatus ofclaim 50, whereinsaid upper portion has an average of about 10 to 20pores per inch and said lower portion has an average of about 30 to 40pores per inch.
 52. The apparatus of claim 44, whereinsaid molten metalpassageway has an inlet portion upstream of said porous media and asettling zone downstream of said inlet portion; and said settling zonehaving sufficient length in relation to the velocity of the molten metalin said settling zone and the depth of said settling zone to allow saidgravity separable liquid particles to float to the top surface of saidmolten metal in said settling zone as said molten metal moves throughsaid settling zone.
 53. The apparatus of claim 52, includinga filtermedia positioned downstream of said porous media to capture suspendedliquid particles remaining in said molten metal after said molten metalis passed through said porous media.
 54. The apparatus of claim 44,includinga filter media positioned downstream of said porous media tocapture suspended liquid particles remaining in said molten metal aftersaid molten metal is passed through said porous media.
 55. An apparatusfor treating molten metal containing suspended liquid particlescomprising:a molten metal passageway; and a porous media that iswettable by said suspended liquid particles mounted generallyhorizontally in said passageway; said porous media constructed andarranged such that said molten metal passes generally upwardly throughsaid porous media; and said porous media having an average of betweenabout 10 to 60 pores per inch.
 56. The apparatus of claim 55,whereinsaid porous media has an average of between about 20 to 40 poresper inch.
 57. The apparatus of claim 55, whereinsaid porous media has anupper portion and a lower portion, said upper portion has less averagepores per inch than the average pores per inch of said lower portion.58. The apparatus of claim 57, whereinsaid upper portion has an averageof about 10 to 20 pores per inch and said lower portion has an averageof about 30 to 40 pores per inch.
 59. The apparatus of claim 55,whereinsaid molten metal passageway has an inlet portion upstream ofsaid porous media and a settling zone downstream of said inlet portion;and said settling zone having sufficient length in relation to thevelocity of the molten metal in said settling zone and the depth of saidsettling zone to allow said gravity separable liquid particles to floatto the top surface of said molten metal in said settling zone as saidmolten metal moves through said settling zone.
 60. The apparatus ofclaim 59, includinga filter media positioned downstream of said porousmedia to capture suspended liquid particles remaining in said moltenmetal after said molten metal is passed through said porous media. 61.The apparatus of claim 55, includinga filter media positioned downstreamof said porous media to capture suspended liquid particles remaining insaid molten metal after said molten metal is passed through said porousmedia.